go to the crystal screen at at the top there will be a tab that says shard crystals, tap that and you will see. You may have enough for a few free premiums if you've been in an alliance, been giving away a bunch in events. How many 3 stars do you have right now? It may be worth just doing the 4 star arena too as most beginners are in the same boat and it doesn't take much to place relatively high, actually less points than the arena in which you use 2 stars at times. The higher end scores are higher but the dropoff after the first hundred or so is steep. Can rack up multiple 3 stars each round instead of just duping it once over the two sets of arenas.